1. Field of the Invention
This invention relates to quantitative measurement of blood flow, and more specifically, quantitative measurement of blood flow using Magnetic Resonance Imaging.
2. Description of Related Art
Imaging of fluid flow within a subject by Magnetic Resonance (MR), has been demonstrated using a variety of techniques based on time-of-flight phenomena and the phenomena of velocity-induced phase shifts. Most of these techniques have been applied to angiography, or the imaging of vascular systems. Techniques for angiography are described by C. L. Dumoulin, H. E. Cline, S. P. Souza, et al. in "Three Dimensional Time-of-Flight Magnetic Resonance Angiography Using Spin Saturation", Magn. Reson. Med., 11:35, 1989, and C. L. Dumoulin, S. P. Souza, M. F. Walker, et al. in "Three Dimensional Phase Contrast Angiography", Magn. Reson. Med., 9:139, 1989, both hereby incorporated by reference.
While the above methods of MR angiography can provide excellent morphological detail, it is frequently difficult to obtain quantitative flow information. This is because a given volume element, known as a volume pixel ("voxel") may contain a distribution of velocities which interfere with one another in the detection or data collection process.
Several non-angiographic techniques have been proposed though they are not common. For example, the use of flow-encoding gradients which provide a motion-dependent phase shift as described in Feinberg D. A., Crooks L. E., Sheldon P., et al. "Magnetic Resonance Imaging the Velocity Vector Components of Fluid Flow" in Mag. Reson. Med. 2:555 (1985), can be used to quantify flow. Fourier-encoded velocity measurements proposed by Feinberg et al. employ a spin-warp imaging pulse sequence which uses flow sensitive phase-encoding gradient pulses to quantify velocity. A modification of the method of Feinberg was disclosed in inventor U.S. patent application Ser. No. 07/651,872 filed Feb. 7, 1991, "Quantitative Measurement of Blood Flow Using Cylindrically Localized Fourier Velocity Encoding" assigned to the present assignee and hereby incorporated by reference.
Feinberg et al. provide a spatial representation of the velocity of flowing blood, but in only a single dimension. There is a need to provide a non-invasive method of determining the flow of fluids in selected vessels and at multiple locations within the same vessel which is accurate and reliable.
In addition, blood flow measurements are a good indication of hemodynamic properties of a given vessel. These hemodynamic properties are important in medical applications in diagnosing a variety of abnormalities and diseases. It would be useful to acquire the hemodynamic properties without the use of invasive techniques.